This invention relates to uniquely structured bodies of revolution and, more particularly, to exact involute ply patterns for use in constructing bodies of revolution from thin sheet material.
Involute construction, formerly known as rosette construction, is a popular approach being used in rocket nozzle technology for the fabrication of exit cones and other bodies of revolution. Such bodies are formed by laminating identical fabric-reinforced composite plies of uniform thickness in such a way that each ply extends to the extremities of the body in both the radial and axial directions. Hence, the boundaries of the body are completely defined by the ply edges. The prior art approach to involute construction incorporates the use of analysis and fabrication techniques that can lead to significant pre-existing flaw distributions within the body. Defects such as wrinkles and fabric distortion are induced and represent the suspected source of numerous failures that have occurred in test firings, and even in fabricated articles prior to imposed loadings. Regions of geometrical discontinuity, such as the neighborhood of a cylinder-cone intersection are particularly sensitive to the formation of this initial damage. The origin of many of these problems appears to lie in the use of an incorrect ply pattern, i.e., the basic ply geometry adopted does not satisfy the involute construction problem, which requires that a prescribed volume of revolution be filled precisely with a given number of identical plies of the same constant thickness.
What is needed in the art, and is not presently available, is the capability to fabricate a body of revolution having no gaps between plies and no wrinkles or distortion of the ply pattern, i.e., having a perfectly smooth and continuous surface.